This invention relates to an improvement of a thin-wall type ball nut of a light-weight type ball screw having a trunnion structure.
In a ball screw having a trunnion structure, a pair of cylindrical trunnion shafts protrude from the outer surface of a ball nut in opposite directions, in such a manner that they have one and the same axis perpendicular to the axis of the ball nut. The ball nut is supported through the trunnion shafts in such a manner that it is rotatable around the axis thereof.
Heretofore, when it is required to reduce the weight of the ball screw of this type, the barrel of the ball nut is decreased in wall thickness.
The conventional thin-wall type ball nut whose barrel is decreased in wall thickness, suffers from the following difficulties: When a great load is applied to the trunnion shafts in the axial direction, the ball nut is liable to be deformed as a whole because the ball nut's barrel is relatively low in rigidity. If the ball nut is deformed in this way, the load is non-uniformly distributed to the steel balls in the ball nut (hereinafter referred to merely as "balls", when applicable); that is, the ball load is locally great, which is one of the factors which may reduce the service life of the ball screw.